Abstract
This paper explains the working principle of the free and open source software “POW” (Photovoltaic Optimization Ware) and shows its application in three fictional examples. The examples show that the sheer annual cumulative irradiation cannot be the only parameter considered when installing a PV system in a building. Furthermore the installation of photovoltaic collectors in the facades of a building can be economically more profitable than on the roof provided that the price [€/kWp] is assumed equal on both the surfaces. This phenomena persists also when combined with a prominent electric storage system. The orientation of the modules in terms of Azimuth loses importance when batteries are installed, but the orientation of the PV module in terms of tilt keeps holding primary importance because it influences the seasonal production profile of the system.